linux-kernel - Re: [PATCH] mm/hmm: remove redundant check non_swap

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Message-ID: <20200612195556.GN65026@mellanox.com>
Date:   Fri, 12 Jun 2020 16:55:56 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm/hmm: remove redundant check non_swap_entry()

On Fri, Jun 12, 2020 at 12:53:23PM -0700, Ralph Campbell wrote:
> 
> On 6/12/20 12:42 PM, Jason Gunthorpe wrote:
> > On Fri, Jun 12, 2020 at 12:35:24PM -0700, Matthew Wilcox wrote:
> > > On Fri, Jun 12, 2020 at 12:26:18PM -0700, Ralph Campbell wrote:
> > > > In zap_pte_range(), the check for non_swap_entry() and
> > > > is_device_private_entry() is redundant since the latter is a subset of the
> > > > former. Remove the redundant check to simplify the code and for clarity.
> > > 
> > > That is highly configuration dependent.
> > > 
> > > #else /* CONFIG_DEVICE_PRIVATE */
> > > ...
> > > static inline bool is_device_private_entry(swp_entry_t entry)
> > > {
> > >          return false;
> > > }
> > 
> > The commit message might be a bit confusing, as it is not a subset, I
> > would say that device_private_entry alone is sufficient to tell if the
> > entry is private or not.
> > 
> > For the !CONFIG_DEVICE_PRIVATE case having it wired to false is
> > right.
> > 
> > Jason
> > 
> 
> How about the following message instead?
> 
> In zap_pte_range(), the check for non_swap_entry() and
> is_device_private_entry() is unnecessary since the latter is sufficient
> to determine if the page is a device private page. Remove the test for
> non_swap_entry() to simplify the code and for clarity.

Yes, that is clearer to me

Jason